Current Limited Load Switch in SOT23 Package
I
LIM
." The maximum current is derived by multiplying
the typical current for the chosen R
SET
in the chart
by 1.25. Some standard resistor values are listed in
Table 1.
Current Device Will Device Always
Limit
Not Current Current Limits
(Typ)
Limit Below
Below
(mA)
(mA)
(mA)
200
250
300
350
400
450
500
550
600
700
800
900
1000
1100
1200
1300
1400
150
188
225
263
300
338
375
413
450
525
600
675
750
825
900
975
1050
250
313
375
438
500
563
625
688
750
875
1000
1125
1250
1375
1500
1625
1750
AAT4611
typical I
LIM
value for 10.5kΩ. Multiplying 0.7A by
0.75 and 1.25 shows that the AAT4611 will limit the
load current to greater than 0.525A but less than
0.875A.
Operation in Current Limit
When a heavy load is applied to the output of the
AAT4611, the load current is limited to the value of
I
LIM
determined by R
SET
(see Figure 2). Since the
load is demanding more current than I
LIM
, the volt-
age at the output drops. This causes the AAT4611 to
dissipate a larger-than-normal quantity of power,
and causes the die temperature to increase. When
the die temperature exceeds an over-temperature
limit, the AAT4611 will shut down until is has cooled
sufficiently, at which point it will start up again. The
AAT4611 will continue to cycle on and off until the
load is removed, power is removed, or until a logic
high level is applied to ON (Pin 4).
R
SET
Ω
(kΩ)
40.2
30.9
24.9
22.1
19.6
17.8
16.2
14.7
13.0
10.5
8.87
7.50
6.81
6.04
5.49
4.99
4.64
Enable Input
In many systems, power planes are controlled by
integrated circuits which run at lower voltages than
the power plane itself. The enable input ON (Pin 4) of
the AAT4611 has low and high threshold voltages that
accommodate this condition. The threshold voltages
are compatible with 5V TTL and 2.5V to 5V CMOS.
Table 1: Current Limit R
SET
Values.
Example: A USB port requires 0.5A. 0.5A multiplied
by 1.33 is 0.665A. From the chart "R
SET
vs. I
LIM
,"
R
SET
should be less than 11kΩ. 10.5 kΩ is a stan-
dard value that is slightly less than, but very close
to, 11kΩ. The chart gives approximately 0.7A as a
Reverse Voltage
The AAT4611 is designed to control current flowing
from IN to OUT. If a voltage is applied to OUT which
is greater than the voltage on IN, large currents may
flow. This could cause damage to the AAT4611.
1
0.75
Output Voltage (V)
0.5
0.25
0
5
4
3
2
1
0
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
Output Current (A)
Output Current
1Ω Load is Turned On at Time = 0
Output Voltage
Time (s)
Figure 2: Overload Operation.
4611.2006.09.1.4
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
